Hello,
It seems like CAD files for whatever reason don't work well with the IR in Corona for C4D. Attached is a screenshot of a regular render and an IR preview. The difference is... noticeable :)
I tried welding the mesh together and I've also made sure that the phong angle is "ok". The same mesh renders perfectly in 3ds Max.
Have fun! :)
Latest Beta (2018-05-30)